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N

non-sparky

Hi people

I have a Rolson 1000 Amps Digital Clamp Meter. I'm not an electrician and hoped for some simple advice.

What I expected to happen was when I put the clamp jaws around a cable I would see a value in Amps. But anything I clamp always comes up 0.00. There is a "lock" button so you can lock the values on screen but this is off. I have tried everything from a kettle lead to a input on a distribution board.

I have tried all of the settings on the dial but I get nothing. The battery is new and the digital display does work, and when you switch the setting dial around the numbers do come up and then settle to 0.00 again.

Am I using the wrong tool or am I using it incorrectly? The cable goes through the loop and the loop closes on itself right??

Thanks for the advice

P
 
Hi,

Yep you are using it wrong!!!

Ok, when current travels down a cable, a magnetic field surrounds it, proportional to the amount of current flowing.

The clamp meter contains a Hall effect chip, which, in lay mans terms, is a magnetic field dependent semi-conductor.

This measures the magnetic field, around the cable, and converts it to a reading on your meter.

However, the current travelling down the phase conductor travels back along the neutral. These currents are equal and opposite, so they cancel each other out - so therefore you you have no manetic field left to measure!!!

So, to measure current with clamp meter, you must clamp aroung either the phase or neutral only!!! Clamping aroung flat twin and earth or a kettle lead will give you zero every time.

A good place to try this would be the cables from your electricity supply meter to your consumer unit (providing you can do this safely)

Also, dont know about your meter, but we used to use Flukes with a plug in clamp

The fluke used to display the result in VOLTAGE, we which we had to convert to CURRENT. There were 2 settings on the clamp, they were 2V = 20A, and 2V = 200A

So if i had it on 2V=200A, i would clamp it around a phase cable, read 1V on the meter, and this would mean 100A flowing in the cable

Job done!!:)
 
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Ha ok, well there you go, thanks!

Ok so that leads me to my next question then, how do I measure the current drawn from a device such as a computer? Is there a simple way? I actually wanted to know what the draw on a UPS was from a server rack without turning the lot off - can it be done?

Cheers for the tech info

non-sparky :)
 
Well yes, you can measure anything PROVIDING that you can seperate ther phase and neutral.

We used to use leads we made ourselves. For the computer you would need to take a spare computer input lead and carefully remove the outersheath (the black pvc covering) exposing the brown (phase) Blue (neutral) and earth (green/yellow) conductors. You just need sufficient to to be able to clamp around the individual phase or neutral (they both carry the same current

You can adapt this to any system by just canabilising whatever lead you want to measure.

Of course, these leads are then ONLY for measurement purposes, not for running the kit normally!

Have fun, and be safe!
 
Thanks Tony, interesting stuff!

Does that mean you can get in-line meters? If not, dibs on a patent!! Makes me wonder why APC (American Power Conversion) don't build them in to the frickin things if its that easy...APC, are you listening???

Cheers mate
 
'In-line' meters were what we used to use before they invented clamps!!!!

Problem was for the meter to measure 100A, it had to be able to handle, well, 100A really! We used to use big metal shunts to reduce the meter size, but then the shunts were big.

Problem with 'in-line' meters as well is you have to disconnect the circuit to connect the meter in. which was a pain in the wotsits.

I remember my first digital clamp meter, got quite emotional i did............:D
 
haha, so I won't become a millionnaire from that idea then!

UPS's should have them built in though, makes so much sense...there's no way I'm cutting up the UPS mains cable to take a reading! So it can't be done without powering down the UPS and getting an electrician in to take it out of the distribution board, then using an in-line meter and powering on 20 servers- that sucks!!

Thanks for your advice, much appreciated, kudos to you!

I was just thinking actually, if you can't measure a "sealed" cable, and you need to use an adapted one with an exposed phase cable which inevitably means have to turn the device off to fit, whats the point in a clamp meter if you have to turn everything off to fit the adapted cable? You would be just as well with an inline meter most of the time surely? Can you get a 3 pin "socket" like one of those timer sockets with an hall effect chip in for numpties like me to measure power consumption in individual servers that have a standard UK plug?

An inline kettle lead meter would be perfect for most of my needs, a male socket on one end and a female socket on the other end. They've got to exist right??

I digress... clamp phase cable only, got it.... :) :)
 
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Ok, that all sounds feasible, but to be honest, when you are pitching it to the team on 'Dragons Den', dont be suprised iff their eyes start to glaze over.........

to be honest, most of the time i have used clamps have been on bigger circuits where we tend to have seperate phase conductors anyway. The cable on your house ring main is 2.5mm squared, I used to work with 70mm squared conductors, then you NEED a clamp to measure the current!!

regards

Tony
 
If it has different settings for current it could also be if set on 1000amp you could clamped around a cable with just 1 amp in it so meter may not read it.
 
Ian, presume you are the same Ian Settle from the IET forums?

I read the posts on the radial off a 32A mcb with the a 13A fuse at the end, I think some of those guys are rude, arrogant and posting for the wrong reasons.

i use this site to learn, and try to share my knowledge with people as much as possible. Too many people use the IET site to try and show how clever they are (or think they are!) and belittling people in the process.

Glad to see you joining in over here, which i find much friendlier!!

regards

Tony
 
haha, so I won't become a millionnaire from that idea then!
Can you get a 3 pin "socket" like one of those timer sockets with an hall effect chip in for numpties like me to measure power consumption in individual servers that have a standard UK plug?

Yes, these do exist. Maplin sell exactly this here: Code L61AQ

Maplin > Plug-In Mains Power and Energy Monitor

They are listing it at £28, but usually have it on special offer for £15. Very useful bit of kit as allong with current (A), it gives you other info such as voltage, wattage, kWh over time, and even power factor.


You can also get special clamp meters that will measure current down multicore cables, so you don't have to split the cable, here:

Megger MMC850 MMC850-EN 100 A multi-core, 200 A single-core Buy Online OR Call

A bit more expensive though at around £100. Still not to bad for a clamp meter though.
 
Thanks Tony, Ian and Martin :) most helpful and I learned some things.

That Energy monitor looks good, I might get a few of them.

The multicore clamp sounds interesting, does that mean you don't need to separate the phase and neutral or have I got the wrong end of the stick?
 
The multicore clamp sounds interesting, does that mean you don't need to separate the phase and neutral or have I got the wrong end of the stick?

Exactly, you can just clamp it round any 3 core mains cable and it will tell you the current flowing. I must say that I have never used one of these clamps, but Megger is a well respected company.
 

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